Origin of Species Variorum

would probably be widely different from what it now is; and the first larval stage certainly would not represent the former condition of any adult and ancient insect.

On the other hand it is highly probable that with many .. animals the embryonic or larval stages .. show us, more or less completely, the state of the ... progenitor of the whole group in its adult condition. In the great class of the Crustacea, forms wonderfully distinct from each other, namely, suctorial parasites, cirripedes, entomostraca, and even the malacostraca, appear at first as larvæ under the nauplius-form; and as these larvæ feed and live in the open sea, and are not adapted for any peculiar habits of life, and from other reasons assigned by Fritz Müller, it is probable that an independent adult animal, resembling the nauplius, .. existed at some very remote period, and subsequently produced, ... along several divergent lines of descent, the several above-named great Crustacean groups. So again it is probable, from what we know of the embryos of mammals, birds, fishes, and reptiles, that these animals are the modified descendants of some one ancient progenitor, which was furnished in its adult state with branchiæ, .. a swim-bladder, four simple limbs, and a long tail, all fitted for an aquatic life.

As all the organic beings, extinct and recent, which have ever lived, can be arranged within a few great classes; and as all within each class have, according to our theory, formerly been connected together by fine gradations, the best, and, if our collections were nearly perfect, the only possible arrangement, would be genealogical; descent being ... the hidden bond of connexion which naturalists have been seeking under the term of the Natural System. On this view we can understand how it is that, in the eyes of most natu- ralists,